Mechanical and chemical-mechanical planarizing processes (collectively "CMP") are used in the manufacturing of electronic devices for forming a flat surface on semiconductor wafers, field emission displays and many other microelectronic-device substrate assemblies. CMP processes generally remove material from a substrate assembly to create a highly planar surface at a precise elevation in the layers of material on the substrate assembly.
FIG. 1 is a schematic isometric view of a web-format planarizing machine 100 that has a support table 102 with a support surface 110 at a workstation defining a planarizing zone. The support surface 110 is generally a rigid panel or plate attached to the table 102 to provide a flat, solid surface to which a portion of a web-format planarizing pad 140 is supported during planarization. The planarizing machine 100 also has a plurality of rollers to guide, position, and hold the web-format pad 140 over the support surface 110. The rollers generally include a supply roller 120, first and second idler rollers 121a and 121b, first and second guide rollers 122a and 122b, and a take-up roller 123. As explained below, a motor (not shown) drives the take-up roller 123, and possibly the supply roller 120, to advance the pad 140 across the support surface 110 along a travel axis T--T. The first idler roller 12 la and the first guide roller 122a also stretch the pad 140 over the support surface 110 to hold the pad 140 during operation.
The planarizing machine 100 also has a carrier assembly 130 to translate a substrate assembly 12 across the pad 140. In one embodiment, the carrier assembly 130 has a substrate assembly holder 132 to pick up, hold and release the substrate assembly 12 at appropriate stages of the planarizing process. The carrier assembly 130 also has a support gantry 134 and a drive assembly 135 that can move along the gantry 134. The drive assembly 135 has an actuator 136, a drive shaft 137 coupled to the actuator 136, and an arm 138 projecting from the drive shaft 137. The aim 138 carries the substrate assembly holder 132 via another shaft 139. The actuator 136 orbits the substrate assembly holder 132 about an axis B--B to move the substrate assembly 12 across the pad 140.
The polishing pad 140 may be a non-abrasive polymeric web (e.g., a polyurethane sheet), or it may be a fixed abrasive polishing pad having abrasive particles fixedly dispersed in a suspension medium. During planarization of the substrate assembly 12, a planarizing fluid 144 flows from a plurality of nozzles 145. The planarizing fluid 144 may be a conventional CMP slurry with abrasive particles and chemicals that etch and/or oxidize the substrate assembly 12, or the planarizing fluid 144 may be a nonabrasive planarizing( solution without abrasive particles. In most CMP applications, abrasive slurries are used on non-abrasive polishing pads, and non-abrasive planarizing solutions are used on fixed abrasive polishing pads.
The planarizing machine 100 incrementally moves the pad 140 across the support surface 110 either during or between planarizing cycles to change the particular portion of the polishing pad 140 in the planarizing zone. For example, the supply and take-up rollers 120 and 123 can drive the polishing pad 140 such that a point P moves incrementally across the support surface 110 to a number of intermediate locations I.sub.1, I.sub.2, etc. Alternatively, the rollers 120 and 123 may drive the polishing pad 140 such that the point P moves all the way across the support surface 110 to completely remove a used portion of the pad 140 from the planarizing zone on the support surface 110. The rollers may also continuously drive the polishing pad at a slow rate such that the point P moves continuously across the support surface 110. Thus, the polishing pad 140 should be free to move axially over the length of the support surface 110 along the travel axis T--T.
CMP processes should consistently and accurately produce a uniform, planar surface on the substrate assembly to enable circuit and device patterns to be formed with photolithography techniques. As the density of integrated circuits increases, it is often necessary to accurately focus the critical dimensions of the photo-patterns to within a tolerance of approximately 0.1 .mu.m. Focusing photo-patterns to such small tolerances, however, is difficult when the planarized surface of the wafer is not uniformly planar. Thus, CMP processes should create a highly uniform, planar surface to be effective.
One processing concern associated with web-format planarizing machines is that the polishing pad 140 may move transversely to the travel axis T--T during a planarizing cycle of the substrate assembly 12. For example, although the first idler roller 121a and the first guide roller 122a stretch the pad 140 over the support surface 110, the orbital motion of the substrate assembly 12 and the friction between the substrate assembly 12 and the pad 140 may cause the pad 140 to move transverse to the travel axis T--T. Such transverse movement of the polishing pad 140 can produce inconsistent planarizing results because it stretches and/or damages the polishing pad 140. The transverse movement of the polishing pad 140 may also allow the slurry to seep underneath the polishing pad 140, which causes uneven wear of the pad 140 and contamination of the planarizing machine 200. Moreover, if the pad wears unevenly, the topography of the pad may cause vibrations in the CMP machine that further affect the planarity of the finished surface and the consistency of the CMP process.